A variety of packages, including dispensing packages or containers, have been developed for personal care products such as shampoo, lotions, etc., as well as for other fluid materials. One type of closure for these kinds of containers typically has a bistable hinge structure connecting a lid to a base mounted over the container opening. The hinge structure has a snap-action biasing force which maintains the lid in a selected closed or open position.
One type of bistable hinge structure incorporated in a closure is disclosed in U.S. Pat. No. 3,135,456. This patent discloses a snap-action hinge structure comprising a thin hinge web joining a base and a lid to accommodate movement of the lid between an open and closed position. The hinge structure has two, spaced-apart pivot axes. In particular, the hinge structure incorporates two, spaced-apart hinges, one hinge having an arcuate configuration connecting the lid to the hinge web and the other hinge having an arcuate configuration connecting the base to the hinge web. The two pivot axes are defined by two parallel lines wherein, at points where the two hinges are closest to each other, one line is tangent to the lid hinge and the other line is tangent to the body hinge.
In contrast, the hinge structure for a cylindrical closure disclosed in U.S. Pat. No. 4,403,712 has a single, main geometric axis hinge and has two webs which each is defined by two hinges which diverge on either side of the web. In commercial embodiments of the cylindrical closure having a single axis hinge structure disclosed in the U.S. Pat. No. 4,403,712, the hinge thickness changes along the length of the hinges. The thickness transition regions can define stress risers which may ultimately have a deleterious effect upon the structure during repeated operation.
Also, in some commercial closures which are sold by Seaquist Closures, 711 Fox Street, Box 20, Mukwanago, Wis. 53149, U.S.A., and which include the single axis hinge structure disclosed in U.S. Pat. No. 4,403,712, the web is provided with an increased thickness region adjacent to the lateral edge of the web.
A snap-action hinge structure with significant improved operating characteristics compared to the hinge structures disclosed in the U.S. Pat. Nos. 3,135,456 and 4,403,712 is a dual axis hinge structure disclosed in the U.S. Pat. No. 5,642,824. The hinge structure is of the type that includes a web having a central portion between two wider ends wherein an arcuate hinge connects the base to the web along one side of the web between the ends and wherein an arcuate hinge connects the lid to the web along another side of the web between the ends. The hinge structure includes at least one abutment surface located so that when the lid is in the closed position, the abutment surface extends adjacent the web central portion from near one of the hinges toward the other hinge. During the closing and opening of the lid, the abutment surface is contacted by the web central portion whereby the position of the web is controlled.
Although the dual axis hinge structure disclosed in U.S. Pat. No. 5,642,824 functions with improved operating characteristics, there are some applications, such as those involving a large number of opening and closing cycles, in which the dual axis hinge structure, as well as other biased hinge structures or bistable, snap-action hinge structures, may be more likely to fail or break.
It is believed that in a snap-action hinge structure which includes a web having a wide end, the stresses are unevenly distributed along the lateral edge of the web end. This is thought to increase the stresses where the lateral edge connects with the closure body and lid. Failure or fracture of such hinge structures is typically initiated at those regions where a lateral edge of the hinge structure web connects with the closure body and/or lid.
Thus, it would be desirable to provide an improved snap-action hinge design in which the stresses in the hinge structure could be more carefully controlled. In particular, it would be beneficial if such an improved design could provide a selected or improved distribution of stress along the outer, lateral edges of the hinge structure.
It would be especially desirable to provide a hinge structure which would have reduced stresses where the hinge structure web lateral edges connect with the closure body and/or lid.
An improved hinge structure design should also permit the hinge structure to provide the desired opening and closing angle range for the lid. A hinge structure with such a capability can provide performance features that are desirable in particular applications.
Also, it would be desirable if such an improved hinge structure could be readily incorporated in a closure that would accommodate efficient, high quality, large volume manufacturing techniques with a reduced product reject rate.
Further, such an improved hinge structure should advantageously accommodate its use in closures with a variety of conventional containers having a variety of conventional container finishes, such as conventional threaded or snap-fit attachment configurations.
The present invention provides an improved hinge structure which can accommodate designs having the above-discussed benefits and features.